Make it not so.
I follow Stewart’s official account on Facebook, and saw the announcement there a few minutes ago, but I was waiting to see confirmation.
One of my very favorite actors, and one of my very favorite celebrities, for his kindness and humanity, as well as for his acting work.
From the Facebook post:
Can’t Q bring him back? 
Wow two Star Trek actors in the same week.
Brian
“Tea,Earl Gray,hot”
Complications from Alzheimers and Lewy Body dementia. Lewy Body dementia is what Robin Williams had.
Stewart is, I believe, the first of TNG’s main cast to pass away.
Alzheimer’s Disease and Lewy Body dementia; both horrible diseases.
I personally refuse to accept the reality of his passing. This hurts too much for me.
Uggh, awful news. I’m not sure if there’s a celebrity whose death would make me sadder.
Sad, but probably better now than later considering what they say he had.
Harrison Ford dying is going to absolutely fuck me up.
So sad. One of my favorite actors. I will miss him.
RIP
- Leondegrance, Guenevere’s Dad in Excalibur.
For me it was Nimoy.
Yes please have Q bring him back! 
I will always remember how he talked on Wait Wait don’t tell me, about watching Galaxy Quest after initially not wanting to and admitting he laughed more than anyone else in the theater.
There was also an interview I saw with Johnathan Frakes where he talked about directing him which was nice:
https://youtu.be/WMuPLrgYTnU?si=nqL3I1bsRRc7_NML
Sadness all around 8[
//i\\
I told my wife that this was the first thing I ever saw Stewart in, and he has been a part of my life since then, appearing in so many things that I’ve been a fan of.
The next thing would have been Dune, then of course ST:TNG. Then countless other things. Just always elevating everything he has ever been in.
What a legend, and what a terrible loss.
Aside from his incredible body of work, I will always remember this video of him (supposedly high) demonstrating the rare “quadruple take.”
He just recently did Sheep Detectives. That seems like a fast downhill slide.
Such a shock.
For me, one of his best roles was as Sejanus in the TV series “I, Claudius”.
But he was awesome in everything he did.
And he never got to play Spider Jerusalem
I’d followed his official page on Facebook for years, and he frequently posted things there – I particularly enjoyed things that he and Ian McKellan shared together, as they were clearly very good friends.
When I went back and looked at Stewart’s account just now, I see that his last post, prior to the announcement of his passing, was in April. So, yeah, very fast.